This application claims priority to Japanese patent application serial number 2001-117576, which was filed on Apr. 17, 2001.
The present invention generally relates to techniques for determining an appropriate timing, for stopping usage of rechargeable batteries before recharging. Such rechargeable batteries may preferably be utilized to drive power tools.
Some known battery-powered devices include means for warning the operator that the rechargeable batteries should be recharged. For example, when the amount of energy that the rechargeable batteries can further supply to the device (hereinafter referred to as xe2x80x9cremaining battery capacityxe2x80x9d) has decreased to a certain level, the means warns the operator of the low remaining battery capacity. Other known battery-powered devices include means for shutting off the supply of current from the rechargeable battery when the battery voltage drops below a certain voltage level.
For example, Japanese Examined Utility Model Publication No. 4-32224 discloses a battery-powered device that actuates a display when the battery voltage has decreased below a reference voltage, thereby advising the operator to recharge the rechargeable batteries. Japanese Laid-open Utility Model Publication No. 5-26278 discloses a battery-powered device that stops the supply of current to a motor when the detected battery voltage has decreased below a predetermined value. In addition, the battery-powered device of Japanese Laid-Open Patent Publication No. 7-1350 stops the flow of current from the rechargeable batteries by turning OFF a switch when the remaining battery capacity has decreased below a predetermined value or when an overload has been applied to the batteries. That is, the switch is turned OFF in order to positively stop the flow of current. Thus, the remaining battery capacity is prevented from further decreasing.
In each of the above-described device, the battery powered device is prevented from being driven using insufficient power, which might cause the work operation to be incompletely performed. In addition, by preventing the rechargeable batteries from being excessively discharged, damage to the rechargeable batteries may be prevented.
However, if rechargeable batteries are charged when the remaining battery capacity is relatively large or high (i.e., it the rechargeable batteries are recharged before the remaining battery capacity has been appropriately reduced), the amount or energy that can be supplied from the fully charged battery (hereinafter referred to as xe2x80x9cfully charged battery capacityxe2x80x9d) may decrease due to xe2x80x9cmemory effects.xe2x80x9d Moreover, if the charging operation is repeatedly performed before the remaining battery capacity has substantially decreased, the fully charged battery capacity will remarkably decrease. Therefore, various techniques have been proposed in order to overcome the problem of memory effects and to prevent a reduction in the fully charged battery capacity.
Generally speaking, the usable life of rechargeable batteries (e.g. nickel-cadmium batteries, nickel metal hydride batteries, etc.) can be prolonged by recharging the batteries before the remaining battery capacity of the batteries has substantially decreased. In other words, if the batteries are permitted to repeatedly and substantially discharge in order to prevent the fully charged battery capacity from decreasing (i.e., to prevent memory effects), the batteries may be irreparably damaged, thereby reducing the usable battery life. However, if the batteries are repeatedly charged before a substantial decrease of the remaining battery capacity in order to prevent damage to the batteries, the fully charged battery capacity generally decreases due to memory effects.
As disclosed in above-mentioned Japanese Examined Utility Model Publication No. 4-32224, Japanese Unexamined Utility Model Publication No 5-26278, and Japanese Unexamined Patent Publication No. 7-1350, battery usage is stopped before the remaining battery capacity has substantially decreased in order to prolong the battery life. However, memory effects will eventually decrease the fully charged battery capacity, thereby reducing the usable life of the battery between changing and discharging at one cycle.
It is, accordingly, one object of the present teachings to teach methods and apparatus that overcome one or more problems of the known art. In one aspect of the present teachings, the fully charged battery capacity of recharageable batteries may be prevented from decreasing due to memory effects without damaging the batteries by excessive discharging, thereby ensuring a long battery life.
In another aspect of the present teachings, apparatus are taught that may include means for detecting the voltage level of the rechargeable batteries. Further, the apparatus may also include means for changing (selecting) a reference voltage level that is utilized for comparison with the detected battery voltage level. The reference voltage level preferably is selected from at least two different reference voltage levels and the selection is preferably based upon use history (or usage history) of the rechargeable batteries.
In another aspect of the present teachings, apparatus also may optionally include means (e.g., audio and/or visual means) for warning an operator that rechargeable batteries, which supply power (current) to a battery-powered device, have been discharged to the selected reference voltage level. As noted above, the reference voltage level can be changed during operation and the reference voltage level is preferably selected based upon use history information of the rechargeable batteries. Thereafter, when the remaining battery capacity has decreased below the selected (or set) reference voltage level, a warning is given to the operator. The reference voltage level is preferably selected so as to prevent damage to the rechargeable batteries due to excessive discharging while also preventing memory effects caused by prematurely recharging the rechargeable batteries. Thus, in accordance with this aspect of the present teachings, the fully charged battery capacity of the rechargeable batteries can be prevented from decreasing due to memory effects and the useful battery life can be prolonged as compared to the known art.
In another aspect of the present teachings, apparatus optionally may include means for stopping (shutting off) the flow of current from the rechargeable batteries to the battery-powered device. The current stopping (shutting off) means optionally may be utilized together with the warning means or instead of the warning means. In this aspect, the flow of current may be stopped, e.g., when the rechargeable batteries have been discharged to the selected reference voltage level. As described further above and below, the reference voltage level can be selected based upon the use history of the rechargeable batteries. In this aspect as well, the fully charged battery capacity of the rechargeable batteries can be prevented from decreasing due to memory effects and the life of the rechargeable batteries can be prolonged.
In another aspect of the present teachings, the means for changing (selecting) the reference voltage, level preferably utilizes a predetermined condition in order to determine whether to change the reference voltage level. For example, when the use story does not satisfy a predetermined condition, priority is given to preventing the usable battery life from decreasing (e.g. preventing damage caused by excessive discharge). On the other hand, when the use history satisfies the predetermined condition, priority is given to preventing the fully charged battery capacity from decreasing due to memory effects. Thus, it is possible not only to prevent the fully charged battery capacity of the rechargeable batteries from decreasing (e.g., due to memory effects), but also to extend the life of the batteries by preventing damage caused by excessive discharge of the batteries.
These aspects and features may be utilized singularly or in combination in order to make improved rechargeable battery packs, battery chargers, power tools and other battery-powered devices and adapters for use with rechargeable battery packs. In addition, other objects, features and advantages of the present teachings will be readily understood after reading the following detailed description together with the accompanying drawings and the claims. Of course, the additional features and aspects disclosed herein also may be utilized singularly or in combination with the above-described aspects and features.